Electroacoustic transducers, such as headphone sets and loudspeakers, are known that convert electrical signals into sounds. Such an electroacoustic transducer includes a driver unit composed of a driver and a diaphragm. To achieve stable operation of the driver unit, required is a space having a sufficient volume and disposed on the side opposite to the side through which the sound emitted from the diaphragm passes. The space is defined by a housing covering the driver unit. The side opposite to the sound emitting side is referred to as a “back side”. The space on the back side in the housing is referred to as a “back space”.
However, an electroacoustic transducer particularly in the form of a headphone set has an insufficient volume of a back space due to demands for design and size reduction in some cases. Such an electroacoustic transducer with an insufficient volume of a back space restricts air stiffness and acoustic design of mass components. The restrictions on the acoustic design increase the sharpness (Q factor) of the driver unit of the electroacoustic transducer. Small electroacoustic transducers, such as headphone sets, earphones, and tabletop loudspeakers, have difficulty exhibiting a smooth frequency response with a high level of sharpness of the driver units.
To solve this problem, an acoustic resistor is known that includes a baffle that has holes and fixes the back side of a diaphragm and acoustic resistors that are composed of felt, for example, and are fit in the holes. The acoustic resistors exhibit acoustic filtering effects.
Japanese Unexamined Patent Application Publication No. 2013-251660 discloses a technique for forming a sound-path space between a flange disposed on the back side of a diaphragm and an acoustic resistor disposed at a predetermined distance from the back surface of the flange in a headphone set.
Unfortunately, even in the above-described electroacoustic transducer having the baffle structure to achieve acoustic filtering effects on the back side of the diaphragm, the frequency response can be improved only in a narrow sound band and thus cannot be improved in a wide sound band.